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* [merged] mm-memcg-slab-fix-memory-leak-at-non-root-kmem_cache-destroy.patch removed from -mm tree
@ 2020-07-24 23:38 akpm
  0 siblings, 0 replies; only message in thread
From: akpm @ 2020-07-24 23:38 UTC (permalink / raw)
  To: cl, guro,, mm-commits, penberg, rientjes,
	shakeelb, songmuchun, stable, vbabka

The patch titled
     Subject: mm: memcg/slab: fix memory leak at non-root kmem_cache destroy
has been removed from the -mm tree.  Its filename was

This patch was dropped because it was merged into mainline or a subsystem tree

From: Muchun Song <>
Subject: mm: memcg/slab: fix memory leak at non-root kmem_cache destroy

If the kmem_cache refcount is greater than one, we should not mark the
root kmem_cache as dying.  If we mark the root kmem_cache dying
incorrectly, the non-root kmem_cache can never be destroyed.  It resulted
in memory leak when memcg was destroyed.  We can use the following steps
to reproduce.

  1) Use kmem_cache_create() to create a new kmem_cache named A.
  2) Coincidentally, the kmem_cache A is an alias for kmem_cache B,
     so the refcount of B is just increased.
  3) Use kmem_cache_destroy() to destroy the kmem_cache A, just
     decrease the B's refcount but mark the B as dying.
  4) Create a new memory cgroup and alloc memory from the kmem_cache
     B. It leads to create a non-root kmem_cache for allocating memory.
  5) When destroy the memory cgroup created in the step 4), the
     non-root kmem_cache can never be destroyed.

If we repeat steps 4) and 5), this will cause a lot of memory leak.  So
only when refcount reach zero, we mark the root kmem_cache as dying.

Fixes: 92ee383f6daa ("mm: fix race between kmem_cache destroy, create and deactivate")
Signed-off-by: Muchun Song <>
Reviewed-by: Shakeel Butt <>
Acked-by: Roman Gushchin <>
Cc: Vlastimil Babka <>
Cc: Christoph Lameter <>
Cc: Pekka Enberg <>
Cc: David Rientjes <>
Cc: Joonsoo Kim <>
Cc: Shakeel Butt <>
Cc: <>
Signed-off-by: Andrew Morton <>

 mm/slab_common.c |   35 ++++++++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 7 deletions(-)

--- a/mm/slab_common.c~mm-memcg-slab-fix-memory-leak-at-non-root-kmem_cache-destroy
+++ a/mm/slab_common.c
@@ -326,6 +326,14 @@ int slab_unmergeable(struct kmem_cache *
 	if (s->refcount < 0)
 		return 1;
+	/*
+	 * Skip the dying kmem_cache.
+	 */
+	if (s->memcg_params.dying)
+		return 1;
 	return 0;
@@ -886,12 +894,15 @@ static int shutdown_memcg_caches(struct
 	return 0;
-static void flush_memcg_workqueue(struct kmem_cache *s)
+static void memcg_set_kmem_cache_dying(struct kmem_cache *s)
 	s->memcg_params.dying = true;
+static void flush_memcg_workqueue(struct kmem_cache *s)
 	 * SLAB and SLUB deactivate the kmem_caches through call_rcu. Make
 	 * sure all registered rcu callbacks have been invoked.
@@ -923,10 +934,6 @@ static inline int shutdown_memcg_caches(
 	return 0;
-static inline void flush_memcg_workqueue(struct kmem_cache *s)
 #endif /* CONFIG_MEMCG_KMEM */
 void slab_kmem_cache_release(struct kmem_cache *s)
@@ -944,8 +951,6 @@ void kmem_cache_destroy(struct kmem_cach
 	if (unlikely(!s))
-	flush_memcg_workqueue(s);
@@ -955,6 +960,22 @@ void kmem_cache_destroy(struct kmem_cach
 	if (s->refcount)
 		goto out_unlock;
+	memcg_set_kmem_cache_dying(s);
+	mutex_unlock(&slab_mutex);
+	put_online_mems();
+	put_online_cpus();
+	flush_memcg_workqueue(s);
+	get_online_cpus();
+	get_online_mems();
+	mutex_lock(&slab_mutex);
 	err = shutdown_memcg_caches(s);
 	if (!err)
 		err = shutdown_cache(s);

Patches currently in -mm which might be from are


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2020-07-24 23:38 [merged] mm-memcg-slab-fix-memory-leak-at-non-root-kmem_cache-destroy.patch removed from -mm tree akpm

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